Tuned ultra high frequency thermionic detector



Oct. 3, 1950 E. G. SCHNEIDER 2,524,179

TUNED ULTRA HIGH FREQUENCY THERMIONIC DETECTOR Filed April 15., 1944 A 11114 111 II awe/Whom EDWlN CMSCHNEIDER Patented Oct. 3, 1950 TUNED ULTRA HIGH FREQUENCY THERM-IONIC DETECTOR Edwin G. Schneider, Watertown, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application April 13, 1944, Serial No. 530,843

12 Claims. 1

This invention relates to detectors for radio signals and particularly to detector apparatus of the thermionic vacuum tube type adapted for operation at very high frequencies such as 1000 megacycles per second and higher. Apparatus according to the present invention is particularly useful at frequencies about 3000 megacycles per second or even higher because it is particularly well adapted to be constructed in a hollow pipe wave guide for detecting oscillations transmitted by said wave guide.

In the past detectors of the thermionic vacuum tube type have been relatively ineificient at the very high frequencies here in question and the inefficiency of the vacuum tube devices has been so great that crystal detectors have been preferred in spite of the greater ruggedness and resistance to overload characteristic of the vacuum tube devices. In accordance with the present invention, an improvement is made in the vacuum tube detector by incorporating therein a resonant circuit of the narrow slit type, thus avoiding the effect of lead inductances and the like. It is an object of the present invention to provide an improved vacuum tube detector having such a resonant circuit incorporated therein and thereby to make it more practical to take advantage of the greater ruggedness and overload handling capability of the vacuum tube devices for highfrequency radio apparatus. It is a further object of the present invention to provide a vacuum tube detector especially adapted for use in a system employing hollow pipe wave guides for the transmission of radio-frequency energy. Still a further object of the present invention is to provide a detector of the above-mentioned type suitable for efiicient heterodyne detection. Still another object of the present invention is to provide a vacuum tube detector of the full wave type.

A typical embodiment of the present invention is illustrated in the drawings in which:

Fig. 1 is an elevation of the vacuum tube structure;

Fig. 2 is a median cross section of the apparatus shown in Fig. 1, and

Fig. 3 is a perspective View, partially diagrammatic, of apparatus of the present invention mounted in a hollow pipe wave guide and arranged for heterodyne detection of signals transmitted in said wave guide.-

The detector apparatus of the present invention is mounted upon a sheet of conducting material, such as sheet copper, shown in the drawings at I. The sheet I is adapted to form a transverse wall in a wave guide 2, which may, in accordance with common practice, be a rectangular pipe wave guide. Good electrical contact is preferably provided between the sheet l and the wave guide 2, especially along the broader sides of the wave guide, and for this reason the sheet 5 is preferably soldered into place. The sheet i has an elongated aperture 3 so dimensioned as to provide a resonant circuit for a desired frequency of operation. The length of the aperture 3 is dependent on the shape of the aperture and on the width of the slit, being adjusted for resonance at the frequency in question with the cathode in place. The long dimension of the aperture is oriented perpendicularly to the direction of the electric vector in the wave guide 2. The ends of the aperture 3 are preferably enlarged as shown in the drawings. This terminal enlargement of the aperture tends to reduce frequency-sensitivity in the device and also provides ample clearance for the supports of the filamentary cathode of the vacuum tube.

The central part of the aperture 3 has the form of a long narrow slit. When oscillations are received in the wave guide having a frequency approximating the resonant frequency of the aperture 3, oscillatory voltages will appear across the central slit portion of the aperture 3, so that the two sides of the aperture may be considered as the two anodes of a full wave rectifier.

The necessary vacuum is maintained in the aperture 3 by means of envelopes 5 and 6, made of glass and sealed to the metal sheet i. preferably by high temperature metal-to-glass seals. Two supporting standards I and 8 are brought through the glass envelope 5, being supported by glass seals 9 and ID. The standards l and 8 project into the vacuum tube to the respective centers of the terminal enlargements of the aper ture 3 and there support the ends of a filamentary cathode l2, which may be a tungsten wire or a suitable oxide coated wire, or the like. The wire l2 thus passes through the middle of the slit portion of the aperture 3. The tuned full wave rectifier vacuum tube thus formed will therefore have closely spaced elements and no extraneous anode leads. Because of the full wave nature of the rectification, the problem of radiofrequency by-passing of the cathode circuit becomes much less critical.

Fig. 3 shows one possible arrangement for utilizing the vacuum tube full wave rectifier of the present invention in connection with awave guide system for obtaining heterodyne detection of signals. The wave guide 2 in which the metal sheet I and its associated structure is located leads in one direction, shown on the right on the drawing, towards the source of signals, which may be a suitable antenna. In the other direction the wave guide 2 leads, through a suitable coupling loop to a coaxial conductor transmission line 16 through which oscillations from a local oscillator may be brought into the system. To the left of the coupling loop [5 the wave guide 2 is provided with a transverse conducting wall I8 the distance of which from the loop l5 and from the sheet I is fixed in accordance with wellknown practice. Filament leads 2!! and 2i are brought in through the wall [8 to connect respectively to the standards 1 and 3. The filament leads 2!) and 2! are provided with sleeve type chokes 22 and 23 consisting of an outer cylinder surrounding the leads and 21 and a piston-like closure, shown respectively at 24 and 25, adapted to make contact with the outer cylinder and with the enclosed lead and thereby to provide a quarter-wave resonator when the position of the closure is properly adjusted. The positions of the closures 24 and 25 may be adjusted by means of the knobs 26 and 21 acting on the tubes 28 and 29. The chokes 22 and 23 serve to prevent radio-frequency energy from leaking out of the wave guide 2 through the leads 20 and 2 l.

One form of output circuit suitable for use with the apparatus shown is indicated diagram- :1

the detected voltage appearing between the cathode i2 and the anode structure I will be periodic and will include a component having a frequency equal to the difference between the local oscillator frequency and the signal frequencies, in accordance with they well-known principles of heterodyne detection. This heterodyne frequency may be made much lower than the signal frequency and may be only approximately 1 per cent thereof. The anode structure I, because of its electrical connection to the wave guide structure 2, is at ground potential with respect to the intermediate or detected frequency. The intermediate-frequency output is therefore obtained from a transformer in the cathode circuit, and since both the cathode leads 20 and 2! are at substantially the same intermediate-frequency potential, the intermediatefrequency output transformer of the detector is provided with a bifilar primary composed of the two similarly wound coils 30 and 3!. A battery provides the necessary heating voltage for the filament i2. Thus the filament heating current passes through the coils 30 and 3| in series but the coils 3G and 3| are effectively in parallel with respect to the intermediate-frequency output of the device. A secondary coil 33, tuned by a variable condenser 34 is provided for exciting a suitable intermediate-frequency amplifier (not shown), forming part of the receiver. As is well known, the intermediate-frequency signal may again be detected after amplification to provide a desired form of indication of the received signals.

The lower end of the coils 30 and 3| of the bifilar primary of the intermediate-frequency transformer are connected to the anode structure (grounded) by a Wire 36 which is preferably connected to the mid-point of the battery 35, although it may be connected at either end of the battery. The lower ends of the coils 30 and 3| are directly connected to the wire 33 through by pass condenser 31 in order to decrease the impedance of the intermediate-frequency circuit. The wire 36 may be connected to the outside of the wave guide structure 2 at any convenient point, theconnection preferably being made in such a manner that the total length of the wire 36 and the distance from the point of connection of the wire 36 and the wave guide to the anode structure I should be kept reasonably small, in order to reduce the intermediatefrequency impedance.

It will be noted that the wires 20 and 2| are brought out of the wave guide 2 in the median plane of the said wave guide which is parallel to the broader side of the Wave guide. The lead wires 20 and 2i may be brought out in other di rections in the said median plane, symmetrical arrangements being preferred. Thus the wires 20 and 2| instead of being brought out through the Wall 18 might be brought out through the narrower metal walls of the wave guide 2, one wire passing through each of said walls. he arrangement shown in Fig. 3 is believed to be more convenient, however. The wires 25 and 2| should be kept at right angles to the direction of the electrical vector in the wave guide 2 in order to prevent the pickup of radio-fre=- quency energy.

It will be apparent upon consideration that the apparatus of the present invention may be provided in a variety of forms all within the spirit of the present invention. As one instance of possible variation, it may be pointed out that the alignment of the filament I2 may be further assured by providing dielectric supports for the standards 1 and 8 between the said standards and the extremities of the aperture Such dielectric supports would then lie within a re gion of small electric field, since the ends of the aperture in the neighborhood of the median plane of the wave guide parallel to the broader sides of the wave guide will be substantially at ground radio-frequency potential. Such supports will,

" however, have the full intermediate-frequency potential impressed across them.

It will also be seen that the whole left end of the wave guide 2 shown in Fig. 3 might be made part 'of' the vacuum system of the apparatus. In such case the nearer half of the envelope 3 might be omitted and suitable vacuum seals might be placed on the transmission line l6 and on the leads 8 and 9.

What I desire to claim and obtain by Letters Patent is:

1. A frequency converter in combination within a hollow pipe wave guide, a unitary transverse conducting partition conductively attached to the walls of said wave guide, said pa Jition having an elongated aperture therein oriented with its long dimension perpendicular to the di rection of the electric vector of oscillations which said wave guide is adapted to transmit, said aperture being dimensioned to provide a circuit resonant at a desired radio-frequency of operation when said apparatus is assembled, evacuated velope means sealed to said partition adapted to maintain a vacuum in said aperture, a thei ionic cathode located in said aperture having terminals passing through and sealed in said envelope means, means for coupling locally generated oscillations to said wave guide in the region of said partition, and leads adapted to conduct cathode heating current and detector output current connected to said terminals and passing out of said wave guide in a path which is everywhere substantially at right angles to said electric vector of said oscillations.

2. Apparatus according to claim 1 including also cylindrical choke resonators on said leads.

3. A frequency converter comprising in combination within a wave guide structure, a transverse conducting partition conductively attached to the walls of said wave guide, said partition having an elongated aperture therein oriented with its long dimension perpendicular to the direction of the electric field of oscillations within said wave guide, said aperture being approximately resonant at the frequency of oscillations within said wave guide, envelope means for maintaining a vacuum in said aperture, a thermionic cathode disposed within said aperture parallel to said long dimension of said aperture and equidistant from the edges of said aperture and havin terminals passing through and supported by said envelope means, means for coupling locally generated oscillatiom to said wave guide in the region of said partition, and leads connected to said terminals for conducting cathode heating current and detector output current.

4. A frequency converter comprising in combination within a rectangular wave guide structure, a rectangular metallic partition disposed transversely of said wave guide in conductive relation with the walls thereof, said partition having an elongated aperture therein oriented with its long dimension parallel to the broad walls of said wave guide, said aperture being approximately resonant at the frequency of oscillations within said wave guide, evacuated envelope means for maintaining a vacuum in said aperture, a substantially linear thermionic cathode disposed within said aperture parallel to the long dimension of said aperture and equidistant from the edges of said aperture and having terminals passing through and supported by said envelope means, means for coupling locally generated oscillations to said wave guide in the region of said partition, and leads connected to said terminals for conducting cathode heating current and detector output current.

5. A frequency converter comprising in combination within a rectangular wave guide structure, a rectangular metallic partition disposed transversely of said wave guide in conductive relation with the walls thereof, said partition being provided with an elongated aperture having substantially circular terminal enlargements, said aperture being centrally located in said partition with its long dimension parallel to the broad walls of said wave guide, said aperture being approximately resonant at the frequency of oscillations within said wave guide, evacuated envelope means secured to said partition for maintaining a vacuum in said aperture, a substantially linear thermionic cathode disposed within said aperture parallel to the long dimension of said aperture and equidistant from the edges of said aperture and terminated at the centers of said terminal enlargements, means for coupling locally generated oscillations to said wave guide in the region of said partition, and leads connected to the terminations of said cathode for conducting heating current and detector output current.

6. A thermionic full-wave detector diode having a unitary anode structure comprising a sheet of conducting material provided with an elongated aperture having enlarged openings at the ends thereof, said aperture being approximately resonant at the frequency of signals adapted to be detected by said diode, and a linear thermionic cathode disposed within said aperture with its axis parallel to and equidistant from the sides of said aperture.

7. A thermionic detector diode adapted for use in a wave guide system including an anode structure comprisin a metallic sheet provided with an elongated aperture having enlarged openings at the ends thereof, said aperture being approximately resonant at the frequency of signals adapted to be detected by said diode, a vacuummaintaining envelope sealed to said sheet to maintain a vacuum in said aperture, and a, substantially linear thermionic cathode disposed within said aperture with its axis parallel to and equidistant from the sides of said aperture.

8. A thermionic detector diode adapted for use in a wave guide system including an anode structure comprising a metallic sheet provided with an elongated aperture having substantially circular terminal enlargements, said aperture being centrally located in said metallic sheet, said aperture being approximately resonant at the.frequency of signals adapted to be detected by said diode, a vacuum-maintaining envelope sealed to said sheet to maintain a vacuum in said aperture, a directly heated thermionic cathode disposed within said aperture with its axis parallel to and equidistant from the sides of said aperture and terminated at the centers of said terminal enlargements, and standards supported by said envelope for maintaining said cathode in position within said aperture.

9. In combination, a rectangular wave guide being closed at one end thereof, means coupled to the other end of said wave guide for energizing said wave guide at a predetermined frequency, a unitary transverse conductin partition conductively attached to the inner walls of said wave guide in spaced relationship with the closed end of said wave guide, said partition having an elongated aperture therein oriented with its long dimension perpendicular to the direction of the electric field vector of oscillations within said wave guide, means for maintaining a vacuum within said aperture, means coupled to said wave guide through a narrow wall thereof between said partition and the closed end of said guide for establishing electromagnetic waves therein at a second predetermined frequency, a thermionic cathode disposed within said aperture parallel to the long dimension of said aperture and equidistant from the edges of said aperture, and means connected to said cathode for deriving a unidirectional voltage which is a function of the resultant of said predetermined frequencies.

10. In combination, a rectangular wave guide, means coupled to one end of said guide for establishing electromagnetic waves therein at a first predetermined frequency, a unitary trans-- verse conducting barrier conductively secured to the inner walls of said wave guide, said barrier having an elongated aperture therein being dimensioned to provide a circuit resonant at said first predetermined frequency, means for maintaining a vacuum within said aperture, means coupled to said wave guide on the opposite side of said barrier from said one end for establishing electromagnetic waves therein at a second predetermined frequency, a linear thermionic cathode disposed within said aperture parallel to the long dimension of said aperture and equidistant from the edges of said aperture, and a 7 pair. of leads. connected to the opposite. ends of saidzcathode for derivinga unidirectional voltage-whichis a function of the resultant of ,said predetermined. frequencies.

11. A thermionic full-wave detector ,diode having a unitarywanode structure comprising a conductive sheet provided with an elongated aperture resonant at the; frequency of signals'adapted to be detected by said.diode,, and a linear thermionic. cathode disposed substantially coextensively within said aperture.

.12. .A full-wave detector diode havin a unitary anode structure comprising a sheet of conducting material having an elongated resonant aperture centrally located therein, and a 1inear thermionic cathode disposedsubstantially coextensively with said aperture with its axis parallel to and equidistant from the sides ofsaid aperture.

EDWIN'G. SCHNEIDER.

REFERENCES CITED The following references are of record in the file of this patent:

Number 20 Number 8 UNITED STATES PATENTS Name Date" Perryman Feb. 10, 1931 McArthur May 24, 1932 Samuel Aug. 15, 1939 Baier et a1. May 21, 1940 Kilgore July 30,1940 Southworth Aug. 26, 1941 Braden Oct. 21, 1941 Linder Aug. 18, 1942 Samuel June 18, 1946 Richmond July 2, 1946 Walt Feb. 10, 1946 Fiskeet a1 Jan. '7, 1947 Fiske Feb. 18, 1947 Lafferty July 1, 1947 Laiferty Nov. 23, 1948 FOREIGN PATENTS Country Date Great Britain Dec..6, 1934 

